First generation infrared (IR) guided missiles could possibly be avoided by pilot manoeuvres that consisted of pointing a targeted aircraft in the direction of the sun to blind the IR missile's detector system or by launching decoy flares onto which the missiles detector would lock and decoy the missile away from the aircraft. Current decoy flares are generally of the pyrotechnic type which produces radiation by combustion of solid pyrotechnic compositions. The most commonly used composition, named MTV composition, is composed of magnesium, Teflon.sup.* and Viton.sup.*. This MTV composition produces a very hot flame and provides an intense point source of IR radiation that should attract this first generation of IR guided missiles. However, advances in missile's IR seekers have significantly reduced the effectiveness of currently fielded pyrotechnic flares. None of the known systems offers the required protection performance against these newer missiles.
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The new generation of IR guided missiles are equipped with one or more electronic counter-countermeasures (CCM) that can discriminate between an aircraft and a decoy, ignoring present aircraft protective countermeasures such as the current decoy flares. New IR guided missiles equipped with spectral CCM have detection systems that can usually distinguish and analyze three bands in the spectral emissions of aircrafts. Therefore, any detected signal in which the band intensities and ratios do not conform to the target aircraft's spectral signature would be recognized as a countermeasure and ignored. Countermeasure flares now would, as a result, have to produce a spectral signature similar to those of aircrafts in order to be effective. This is not the case with present pyrotechnic flares. Pyrotechnic flare's spectral signature are, in fact, very different from that of an aircraft because they emit principally in the first spectral band that would be analyzed by newer guided missiles IR seeker equipped with spectral CCM, whereas a jet aircraft's signature shows high intensities in the second and third bands. This spectral mismatched signature generally limits the usefulness of current pyrotechnic flares to the previous generation of IR guided missiles.
Operational analysis, based on measured experimental flare performance, show that pyrophoric flares offer a strong potential to provide the required performance to decoy the newer generation of IR seeking missiles. The spectral signature of a pyrophoric liquid, such as alkyl aluminum compounds that burn spontaneously when sprayed into the air, more closely resemble a jet aircraft's spectral signature so that an IR seeking missile would not recognize that type of flare as a countermeasure.
The basic functioning principles of any pyrophoric flare would have very little in common to the existing pyrotechnic flares except for the fact that they are both ejected from a launcher by an impulse cartridge. A pyrophoric flare would require a liquid in a perfectly sealed reservoir since pyrophoric liquids react and burn on exposure to air using the oxygen of the air as an oxidant. Pyrotechnic flares, on the other hand, use a solid grain composition contained in a protective shell. Some means would be required in a pyrophoric flare to eject the pyrophoric liquid through a calibrated nozzle such as a gas generator to provide a certain pressure profile inside the flare to break rupturing discs and eject the liquid. Therefore, a high stress resistance container and special sealing component attachments would be required for a pyrophoric flare. These items are not required for a pyrotechnic flare. In addition, mobile and/or removable components of the ignition system for any pyrophoric flare would require special sealing devices to prevent any pressure leaks through the ignition system during the whole functioning of the flare. This is not a concern for a pyrotechnic flare. Furthermore, pyrophoric liquids, such as alkyl aluminum compounds, are incompatible with many materials and especially with most polymers. These constraints require a completely new design for pyrophoric flares such as that described in U.S. Pat. No. 5,631,441 which issued on the 20.sup.th of May 1997.
The decoy flare described in U.S. Pat. No. 5,631,441 comprises a tubular container for pyrophoric liquid with a nozzle at one end which is normally separated from pyrophoric liquid in the container by a rupturing disc, the other end of the container being provided with a mechanism to apply pressure to the pyrophoric liquid. That pressure is transferred by the liquid to the rupturing disc that will rupture at a predetermined pressure and result in the pyrophoric liquid being ejected through the nozzle into the atmosphere where the pyrophoric liquid burns on exposure to the air. The nozzle configuration shown in U.S. Pat. No. 5,631,441 was a straight hole drilled through a nozzle cap. This nozzle design is very effective for high flow rates of the pyrophoric liquid fuel under all conditions. High flow rates result in short burn times for a flare. The flow rate of the pyrophoric liquid through this nozzle is dependent on the pressure on the liquid and diameter of the straight nozzle. That type of nozzle was, however, found to be less effective and not appropriate for low flow rates of the pyrophoric liquid that may be desired in order to provide longer burning times and, in particular, for low flow rates at high altitudes. It is assumed that this less effective performance for low flow rates at high altitudes is due to a reduced concentration of pyrophoric liquid fuel being sprayed into a very cold air (less reactive) environment having a substantially reduced quantity of reactive oxygen.